Man has long battled bacterial infections, and no one can doubt the tremendous successes obtained. Before the discovery and development of antibiotics, death due to a bacterial infection was frequently rapid and inevitable. Surgical procedures and sanitary conditions have vastly improved from the time when amputation was associated with a 50 percent mortality rate.
Nonetheless, the battle has not been won. Undoubtedly a significant part of the problem is that bacteria are the product of nearly 3 billion years of natural selection from which they have emerged as an immensely diverse group of organisms that colonize almost all parts of the world and its inhabitants. To begin to understand bacteria requires categorization, and the most fundamental categories for bacteria are their response to the Gram stain, yielding (for the most part) Gram positive bacteria and Gram negative bacteria.
The difference in response to the Gram stain results from differences in bacterial cell walls. The cells walls of Gram negative bacteria are made up of a unique outer membrane of two opposing phospholipid-protein leaflets, with an ordinary phospholipid in the inner leaflet but the extremely toxic lipopolysaccharide in the outer leaflet. The cell walls of Gram positive bacteria seem much simpler in comparison, containing two major components, peptidoglycan and teichoic acids plus additional carbohydrates and proteins depending on the species.
Of the Gram positive bacteria, one of the most common genera is Staphylococcus. Staphylococci commonly colonize humans and animals and are an important cause of human morbidity and mortality, particularly in hospitalized patients. Staphylococci are prevalent on the skin and mucosal linings and, accordingly, are ideally situated to produce both localized and systemic infections.
There are two main groups of Staphylococci divided according to the production of “coagulase,” an enzyme that causes fibrin to coagulate and to form a clot: coagulase positive and coagulase negative. The coagulase positive Staphylococcus species most frequently pathogenic in humans is Staphylococcus aureus. S. aureus is the most virulent Staphylococcus and produces severe and often fatal disease in both normal and immunocompromised hosts. Staphylococcus epidermidis is the most common coagulase negative species.
In recent years, S. epidermidis has become a major cause of nosocomial infection in patients whose treatments include the placement of foreign objects such as cerebrospinal fluid shunts, cardiac valves, vascular catheters, joint prostheses, and other implants into the body. S. epidermidis and S. aureus are common causes of post-operative wound infections and S. epidermidis has also become a common cause of peritonitis in patients with continuous ambulatory peritoneal dialysis. In a similar manner, patients with impaired immunity and those receiving parenteral nutrition through central venous catheters are at high risk for developing S. epidermidis sepsis. (C. C. Patrick, J. Pediatr., 116:497 (1990)). S. epidermidis is now recognized as a common cause of neonatal nosocomial sepsis. Infections frequently occur in premature infants that have received parenteral nutrition which can be a direct or indirect source of contamination.
Staphylococcal infections are difficult to treat for a variety of reasons. Resistance to antibiotics is common and becoming more so. See L. Garrett, The Corning Plague, “The Revenge of the Germs or Just Keep Inventing New Drugs” Ch. 13, pgs. 411-456, Farrar, Straus and Giroux, N.Y., Eds. (1994). In one study, the majority of Staphylococci isolated from blood cultures of septic infants were multiply resistant to antibiotics (A. Fleer et al., Pediatr. Infect. Dis. 2:426 (1983)). A more recent study describes methicillin-resistant S. aureus (J. Romero-Vivas, et al., Clin. Infect. Dis. 21:1417-23 (1995)) and a recent review notes that the emergence of antibiotic resistance among clinical isolates makes treatment difficult (J. Lee., Trends in Micro. 4(4):162-66 (April 1996). Recent reports in the popular press also describe troubling incidents of antibiotic resistance. See The Washington Post “Microbe in Hospital Infections Show Resistance to Antibiotics,” May 29, 1997; The Washington Times, “Deadly bacteria outwits antibiotics,” May 29, 1997.
In addition, host resistance to Staphylococcal infections is not clearly understood. Opsonic antibodies have been proposed to prevent or treat Staphylococcal infections. See U.S. Pat. No. 5,571,511 to G. W. Fischer issued Nov. 5, 1996, specifically incorporated by reference. The microbial targets for these antibodies have been capsular polysaccharides or surface proteins. As to capsular polysaccharides, the immunization studies of Fattom et al., J. Clin. Micro. 30(12):3270-3273 (1992) demonstrated that opsonization was related to S. epidermidis type-specific anti-capsular antibody, suggesting that S. epidermidis and S. aureas have a similar pathogenesis and opsonic requirement as other encapsulated Gram positive cocci such as Streptococcus pneumonia. As to surface proteins, Timmerman, et al., J. Med. Micro. 35:65-71 (1991) identified a surface protein of S. epidermidis that was opsonic for the homologous strain used for immunization and for monoclonal antibody production. While other monoclonal antibodies were identified that bound to non-homologous S. epidermidis strains, only the monoclonal antibody produced to the homologous strain was opsonic and opsonization was enhanced only to the homologous strain but not to heterologous strains. Accordingly, based on the studies of Fattom et al., and Timmerman et al., and others in the field (and in contrast to our own studies), one would not expect that an antibody that is broadly reactive to multiple strains of S. epidermidis and to S. aureus would have opsonic activity against both. This is particularly true for antibodies that bind to both coagulase positive and coagulase negative Staphylococci.
Accordingly, there is a need in the art to provide monoclonal antibodies that can bind to Staphylococcus of both coagulase types and that can enhance phagocytosis and killing of the bacteria and thereby enhance protection in vivo. There is also a need in the art for the epitope of the site to which such antibodies can bind so that other antibodies with similar abilities can be identified and isolated.
There is a related need in the art for humanized or other chimeric human/mouse monoclonal antibodies. In recent well publicized studies, patients administered murine anti-TNF (tumor necrosis factor) monoclonal antibodies developed anti-murine antibody responses to the administered antibody. (Exley A. R., et al., Lancet 335:1275-1277 (1990)). This type of immune response to the treatment regimen, commonly referred to as the HAMA response, decreases the effectiveness of the treatment and may even render the treatment completely ineffective. Humanized or chimeric human/mouse monoclonal antibodies have been shown to significantly decrease the HAMA response and to increase the therapeutic effectiveness. See LoBuglio et al., P.N.A.S. 86:4220-4224 (June 1989).